check if a jsonNode contains a specific key then EXTRACT its value once it exists

Question

I have this String an I covered it to jsonNode using the ObjectMapper. Then I tried to look for a pecific key in this jsonNode so I used the ".has" but it did not work !! Here is what I did :

{ 
    "links": {
        "data": {
            "self": {
                "body": "", 
                "content_type": "",
                "href": "/api/v2/nodes",
                "method": "POST", 
                "name": "" 
            } 
        }
    },
    "results": { 
        "data": {
            "properties": { 
                "container": true,
                "container_size": 0,
                "create_date": "2020-06-22T16:19:07",
                "create_user_id": 1000,
                "description": ""
                "description_multilingual": { 
                    "en": "",
                    "fr_FR": "" 
                },
                "external_create_date": null,
                "external_identity": "",
                "external_identity_type": "",
                "external_modify_date": null,
                "external_source": "",
                "favorite": false,
                "id": 276625,
                "mime_type": null,
                "modify_date": "2020-06-22T16:19:07",
                "modify_user_id": 1000,
                "name": "mar",
                "name_multilingual": {
                    "en": "mar",
                    "fr_FR": ""
                },
                "owner": "Admin",
                "owner_group_id": 1001,
                "owner_user_id": 1000,
                "parent_id": 2000,
                "permissions_model": "advanced",
                "reserved": false,
                "reserved_date": null,
                "reserved_shared_collaboration": false,
                "reserved_user_id": 0,
                "size": 0,
                "size_formatted": "0 Eléments",
                "type": 0,
                "type_name": "Dossier",
                "versions_control_advanced": false,
                "volume_id": -2000 
            } 
        } 
    }
}

and I want to test whether it has the "id" key (it actually exists in line 31) so I used .has() as mentioned in How to check if a json key exists?:

ObjectMapper mapper = new ObjectMapper();    
JsonNode rootNode= mapper.readTree(body);
         if(rootNode.has("id")){
            System.out.println(true);
         }
        else{
            System.out.println(false);
        }

but always it shows me "false" as output !!

Answer 1

If you're trying to find a key which is placed inside nested object, you may use findValue(String key) method which returns null if a value is not found by the given key:

ObjectMapper mapper = new ObjectMapper();
JsonNode rootNode= mapper.readTree(json);

String[] keys = {
    "id", "create_date", "versions_control_advanced", "name", "nofield"
};

for (String key : keys) {
    JsonNode value = rootNode.findValue(key);
    System.out.printf("Key %s exists? %s --> value=%s%n", key, value != null,
                    value == null ? null : value.asText());

}

Output:

Key id exists? true --> value=276625
Key create_date exists? true --> value=2020-06-22T16:19:07
Key versions_control_advanced exists? true --> value=false
Key name exists? true --> value=
Key nofield exists? false --> value=null